U.S. patent application number 13/259962 was filed with the patent office on 2012-01-19 for fuel cell system.
This patent application is currently assigned to TOYOTA JIDOSHA KABUSHIKI KAISHA. Invention is credited to Tomotaka Ishikawa, Hiromi Tanaka, Osamu Yumita.
Application Number | 20120015269 13/259962 |
Document ID | / |
Family ID | 43356050 |
Filed Date | 2012-01-19 |
United States Patent
Application |
20120015269 |
Kind Code |
A1 |
Ishikawa; Tomotaka ; et
al. |
January 19, 2012 |
FUEL CELL SYSTEM
Abstract
Provided is a fuel cell system that performs a warm-up operation
by reducing a supply of oxidant gas to a fuel cell, the system
having: a fuel cell; and a control unit that regulates amounts of
oxidant gas and fuel gas supplied to the fuel cell and controls a
power-generation state of the fuel cell. During the warm-up
operation with a reduced supply of oxidant gas to the fuel cell,
the control unit varies a voltage of the fuel cell for a short
period of time to obtain current-voltage characteristics which
indicate a relationship of an output voltage and an output current
of the fuel cell, calculates an effective catalyst area of the fuel
cell based on the obtained current-voltage characteristics, and
determines whether the warm-up operation of the fuel cell can be
stopped or not based on the calculated effective catalyst area.
Inventors: |
Ishikawa; Tomotaka;
(Toyota-shi, JP) ; Tanaka; Hiromi; (Toyota-shi,
JP) ; Yumita; Osamu; (Nagoya-shi, JP) |
Assignee: |
TOYOTA JIDOSHA KABUSHIKI
KAISHA
Toyota-shi
JP
|
Family ID: |
43356050 |
Appl. No.: |
13/259962 |
Filed: |
June 19, 2009 |
PCT Filed: |
June 19, 2009 |
PCT NO: |
PCT/JP2009/061222 |
371 Date: |
September 23, 2011 |
Current U.S.
Class: |
429/431 |
Current CPC
Class: |
H01M 8/04768 20130101;
H01M 8/04268 20130101; H01M 8/04589 20130101; H01M 8/04753
20130101; Y02E 60/50 20130101; H01M 8/04731 20130101; H01M 8/0488
20130101; H01M 8/04992 20130101; H01M 8/04559 20130101 |
Class at
Publication: |
429/431 |
International
Class: |
H01M 8/04 20060101
H01M008/04 |
Claims
1. A fuel cell system that performs a warm-up operation by reducing
an amount of oxidant gas supplied to a fuel cell, the system
comprising: a fuel cell; and a control unit that regulates amounts
of oxidant gas and fuel gas supplied to the fuel cell and controls
a power-generation state of the fuel cell, wherein, during the
warm-up operation with a reduced supply of oxidant gas to the fuel
cell, the control unit varies a voltage of the fuel cell for a
short period of time to obtain current-voltage characteristics
which indicate a relationship of an output voltage and an output
current of the fuel cell, and wherein the control unit calculates
an effective catalyst area of the fuel cell based on the obtained
current-voltage characteristics and determines whether the warm-up
operation of the fuel cell can be stopped or not based on the
calculated effective catalyst area.
2. The fuel cell system according to claim 1, wherein the control
unit determines, based on the calculated effective catalyst area,
whether circulation in an anode circulation system is allowed or
not, the anode circulation system being a system for supplying fuel
gas to the fuel cell in a circulating manner.
3. The fuel cell system according to claim 1, wherein the control
unit determines, based on the calculated effective catalyst area,
whether circulation in a cooling system for the fuel cell is
allowed or not.
Description
TECHNICAL FIELD
[0001] The present invention relates to a fuel cell system which
performs, when it is started at a temperature below zero, a warm-up
operation by reducing a supply of oxidant gas to a fuel cell.
BACKGROUND ART
[0002] Among fuel cells generating electric power utilizing an
electrochemical reaction between hydrogen and oxygen, polymer
electrolyte fuel cells are known. A polymer electrolyte fuel cell
of this type has a stack which is constituted by a plurality of
stacked cells. Each cell constituting the stack has an anode (fuel
electrode) and a cathode (air electrode), and a solid polymer
electrolyte membrane having a sulfonic acid group as an ion
exchange group is disposed between the anode and the cathode.
[0003] A fuel gas (hydrogen-enriched reformed hydrogen obtained by
reforming hydrogen gas or hydrocarbon) is supplied to the anode,
while an oxidant gas (e.g., air) that contains oxygen as an oxidant
is supplied to the cathode. Upon the supply of the fuel gas to the
anode, hydrogen contained in the fuel gas reacts with a catalyst in
a catalyst layer of the anode, resulting in the generation of
hydrogen ions. The generated hydrogen ions pass through the solid
polymer electrolyte membrane and electrically react with oxygen in
the cathode. Through this electrochemical reaction, electric power
is generated.
[0004] In a fuel cell system that utilizes a polymer electrolyte
fuel cell as a power source, if the system stops the operation, the
temperature of the fuel cell decreases, and the water within the
fuel cell, which has been in hot and humid conditions until then,
would condense to form dew drops, or freeze. In particular, when
the temperature of the fuel cell is below zero, the water generated
through the power-generation reaction freezes on the surface of the
electrode, which would interfere with the supply of oxygen and
inhibit the power-generation reaction.
[0005] So, when starting the system at a temperature below zero, a
warm-up operation is performed in which an amount of oxidant gas
supplied to the fuel cell is reduced to increase an amount of heat
generation (see Patent Document 1 below). Also, in order to reduce
problems that would occur when the fuel cell has a negative voltage
with insufficient hydrogen gas during such a warm-up operation, a
fuel cell system as described in Patent Document 2 below has been
proposed.
[0006] In the technique described in Patent Document 2, a fuel cell
system is controlled using a flowchart illustrated in FIG. 2 of the
document. According to the flowchart in FIG. 2 of Patent Document
2, a warm-up operation is performed if the fuel cell is at a
temperature of 0.degree. C. or lower, and stopped if the
temperature goes above 0.degree. C.
PRIOR ART REFERENCES
Patent Documents
[0007] Patent Document 1: Japanese laid-open patent publication No.
2004-30979
[0008] Patent Document 2: Japanese laid-open patent publication No.
2008-198439
SUMMARY OF THE INVENTION
Problem to be Solved by the Invention
[0009] A fuel cell (fuel cell stack) has a large heat capacity, and
it takes time to warm up all portions of the fuel cell (fuel cell
stack). Also, even if the portion for which the temperature was
measured has a temperature exceeding 0.degree. C., the possibility
that ice remains in a gas flow path and causes clogging there
cannot be ignored, and in view of this, it would not always be
appropriate to stop a warm-up operation simply based on the fact
that the temperature of the fuel cell is above 0.degree. C.
[0010] The present invention has been made considering the problems
described above, and an object of the invention is to provide a
fuel cell system that performs, when it is started at a temperature
below zero, a warm-up operation by reducing a supply of oxidant gas
to a fuel cell, the system being capable of accurately finding
whether a gas flow path is in a clogged state or not so that the
start and stop of the warm-up operation can be appropriately
judged.
Means for Solving the Problem
[0011] In order to achieve the above object, the invention provides
a fuel cell system that performs a warm-up operation by reducing an
amount of oxidant gas supplied to a fuel cell, the system having: a
fuel cell; and a control unit that regulates amounts of oxidant gas
and fuel gas supplied to the fuel cell and controls a
power-generation state of the fuel cell, wherein, during the
warm-up operation with a reduced supply of oxidant gas to the fuel
cell, the control unit varies a voltage of the fuel cell for a
short period of time to obtain current-voltage characteristics
which indicate a relationship of an output voltage and an output
current of the fuel cell, and wherein the control unit calculates
an effective catalyst area of the fuel cell based on the obtained
current-voltage characteristics and determines whether the warm-up
operation of the fuel cell can be stopped or not based on the
calculated effective catalyst area.
[0012] According to the invention, while a warm-up operation is
being performed by reducing an amount of oxidant gas supplied to
the fuel cell, the voltage of the fuel cell is varied for a short
period of time; in other words, a current sweep is performed for
the fuel cell for a short period of time. When performing a current
sweep for the fuel cell for a short period of time, an output
current increases together with a decrease of voltage because an
oxide coating peels off the catalyst, but after that, the output
current decreases due to the oxidation of the catalyst, and by
increasing the voltage thereafter, the fuel cell returns to the
voltage-current relationship at the point it originated. Since the
thus obtained current-voltage characteristics are almost the same
as the cyclic voltammetry (CV) curve of the unit cell constituting
the fuel cell, an area corresponding to an area of oxidation
current in the CV curve can be obtained from the obtained
current-voltage characteristics, and the effective catalyst area
can consequently be obtained. Accordingly, in this invention, the
effective catalyst area of the fuel cell is calculated by varying
the voltage of the fuel cell for a short period of time, and the
calculated effective catalyst area is used to accurately determine
whether the gas flow path of the fuel cell is clogged or not,
thereby determining whether the warm-up operation of the fuel cell
can be stopped or not.
[0013] In the fuel cell system according to the invention, it is
preferable that the control unit determines, based on the
calculated effective catalyst area, whether circulation in an anode
circulation system is allowed or not, the anode circulation system
being a system for supplying a fuel gas to the fuel cell in a
circulating manner. Since whether the gas flow path of the fuel
cell is clogged or not can accurately be determined by calculating
the effective catalyst area, the circulation in the anode
circulation system can be stopped when the flow path in the anode
circulation system is considered to be frozen. It is considered
that the clogging in the gas flow path of the fuel cell is due to
freezing, and thus, further clogging can be suppressed by stopping
the circulation in the anode circulation system in the above
manner.
[0014] In the fuel cell system according to the invention, it is
also preferable that the control unit determines, based on the
calculated effective catalyst area, whether circulation in a
cooling system for the fuel cell is allowed or not. Even in the
case where the circulation in the cooling system is stopped to
perform the warm-up operation more efficiently, since whether the
gas flow path of the fuel cell is clogged or not can accurately be
determined by calculating the effective catalyst area, the
circulation in the cooling system can be started if the effective
catalyst area becomes equal to or greater than a predetermined
value.
EFFECT OF THE INVENTION
[0015] The invention can provide a fuel cell system that can
accurately find whether a gas flow path is in a clogged state or
not and can thus appropriately judge the start and stop of a
warm-up operation.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a diagram illustrating the configuration of a fuel
cell system to be installed in a fuel cell vehicle according to an
embodiment of the invention.
[0017] FIG. 2 is a flowchart for determining whether a warm-up
operation is allowed to be stopped or not in the fuel cell system
shown in FIG. 1.
[0018] FIG. 3 is a chart indicating one example of the
current-voltage characteristics of a fuel cell obtained based on
the flowchart shown in FIG. 2.
[0019] FIG. 4 is a chart showing one example of the CV curve of a
unit cell which constitutes a fuel cell.
[0020] FIG. 5 is a flowchart for determining whether the
circulation in a fuel gas supply system is allowed or not in the
fuel cell system shown in FIG. 1.
[0021] FIG. 6 is a flowchart for determining whether the
circulation in a cooling system is allowed or not in the fuel cell
system shown in FIG. 1.
MODE FOR CARRYING OUT THE INVENTION
[0022] Embodiments of the invention will be described below with
reference to the attached drawings. In order that the description
can easily be understood, the same components are given the same
reference numerals to the extent possible in the respective
drawings, and any repetitive description will be omitted.
[0023] First, a fuel cell system FCS to be installed in a fuel cell
vehicle according to an embodiment of the invention will be
described with reference to FIG. 1. FIG. 1 is a diagram showing the
system configuration of a fuel cell system FCS that functions as an
on-vehicle power source system of a fuel cell vehicle. The fuel
cell system FCS can be installed in vehicles such as fuel cell cars
(FCHV), electric cars or hybrid cars.
[0024] The fuel cell system FCS has: a fuel cell FC; an oxidant gas
supply system ASS; a fuel gas supply system FSS (anode circulation
system); an electric power system ES; a cooling system CS; and a
controller EC. The fuel cell FC receives the supply of reactant
gases (fuel gas, oxidant gas) and generates electric power. The
oxidant gas supply system ASS is a system for supplying air as an
oxidant gas to the fuel cell FC. The fuel gas supply system FSS is
a system for supplying hydrogen gas as a fuel gas to the fuel cell
FC. The electric power system ES is a system for controlling
electric power charge/discharge. The cooling system CS is a system
for cooling the fuel cell FC. The controller EC is a controller for
the overall control of the entire fuel cell system FCS.
[0025] The fuel cell FC is structured as a solid polymer
electrolyte type cell stack formed of a number of cells (each unit
cell having (as a power generator) an anode, a cathode and
electrolyte) stacked in series. In the fuel cell FC under a normal
operation, the oxidation reaction shown by formula (1) occurs in
the anode and the reduction reaction shown by formula (2) occurs in
the cathode, and in the fuel cell FC as a whole, the electrogenic
reaction shown by formula (3) occurs.
H.sub.2.fwdarw.2H.sup.++2e.sup.- (1)
(1/2)O.sub.2+2H.sup.++2e.sup.-.fwdarw.H.sub.2O (2)
H.sub.2+(1/2)O.sub.2.fwdarw.H.sub.2O (3)
[0026] The oxidant gas supply system ASS has an oxidant gas flow
path AS3 and an oxidant-off gas flow path AS4. The oxidant gas flow
path AS3 is a flow path through which the oxidant gas to be
supplied to the cathode of the fuel cell FC flows. The oxidant-off
gas flow path AS4 is a flow path through which the oxidant-off gas
discharged from the fuel cell FC flows.
[0027] The oxidant gas flow path AS3 is provided with an air
compressor AS2 and a humidifier AS5. The air compressor AS2 is a
compressor for introducing the oxidant gas from the atmosphere
through a filter AS1. The humidifier AS5 is a device for
humidifying the oxidant gas compressed by the air compressor
AS2.
[0028] The oxidant-off gas flow path AS4 is provided with a
pressure sensor S6, a back pressure regulating valve A3 and the
humidifier AS5. The back pressure regulating valve A3 is a valve
for regulating the oxidant gas supply pressure. The humidifier AS5
is provided as a device for exchanging moisture between the oxidant
gas (dry gas) and the oxidant-off gas (wet gas).
[0029] The fuel gas supply system FSS has a fuel gas supply source
FS1, a fuel gas flow path FS3, a circulation flow path FS4, a
circulation pump FS5 and an exhaust/drain flow path FS6. The fuel
gas flow path FS3 is a flow path through which the fuel gas to be
supplied from the fuel gas supply source FS1 to the anode of the
fuel cell FC flows. The circulation flow path FS4 is a flow path
for returning the fuel-off gas discharged from the fuel cell FC
back to the fuel gas flow path FS3. The circulation pump FS5 pumps
the fuel-off gas within the circulation flow path FS4 into the fuel
gas flow path FS3. The exhaust/drain flow path FS6 is a flow path
connected to and branching from the circulation flow path FS4.
[0030] The fuel gas supply source FS1 is constituted by, for
example, a high-pressure hydrogen tank or a hydrogen absorbing
alloy, and stores hydrogen gas at a high pressure (e.g., 35 MPa to
70 MPa). When a cutoff valve H1 is opened, the fuel gas flows to
the fuel gas flow path FS3 from the fuel gas supply source FS1. The
pressure of the fuel gas is reduced, for example, to approximately
200 kPa by a regulator H2 or an injector FS2, and the resultant gas
is supplied to the fuel cell FC.
[0031] The fuel gas flow path FS3 is provided with the cutoff valve
H1, the regulator H2, the injector FS2, a cutoff valve H3, and a
pressure sensor S4. The cutoff valve H1 is a valve for blocking or
allowing the fuel gas supply from the fuel gas supply source FS1.
The regulator H2 is provided for regulating the pressure of fuel
gas. The injector FS2 is provided for controlling the amount of
fuel gas supplied to the fuel cell FC. The cutoff valve H3 is a
valve for blocking the fuel gas supply to the fuel cell FC.
[0032] The regulator H2 is a device for regulating the pressure on
the upstream side (primary pressure) to a preset secondary
pressure, and is constituted by, for example, a mechanical pressure
reducing valve for reducing the primary pressure. The mechanical
pressure reducing valve has a casing in which a backpressure
chamber and a pressure regulating chamber are formed while being
separated by a diaphragm, and has a configuration in which, with
the backpressure in the backpressure chamber, the primary pressure
is reduced to a predetermined pressure in the pressure regulating
chamber, thereby obtaining the secondary pressure. By arranging the
regulator H2 on the upstream side of the injector FS2, the
upstream-side pressure of the injector FS2 can effectively be
reduced.
[0033] The injector FS2 is an electromagnetic drive type on-off
valve having a configuration in which a valve body is directly
driven by an electromagnetic driving force with a predetermined
drive period so as to be separated from a valve seat, thereby
controlling a gas flow rate or a gas pressure. The injector FS2 is
provided with: a valve seat having an injection hole through which
gaseous fuel such as fuel gas is injected; a nozzle body for
supplying and guiding the gaseous fuel to the injection hole; and a
valve body held so as to be contained in a manner such that the
valve body is moveable in an axial direction (gas flow direction)
with respect to the nozzle body, for opening and closing the
injection hole.
[0034] The valve body of the injector FS2 is driven by a solenoid,
which is an electromagnetic drive, and is configured such that
control signals that are output from the controller EC can control
a gas injection duration and a gas injection time of the injector
FS2. In order to supply gas to the downstream thereof at a required
flow rate, the injector FS2 changes at least one of the opening
area (degree of opening) and the opening period of time of the
valve body, which is provided in a gas flow path of the injector
FS2, thereby adjusting the flow rate (or hydrogen mol
concentration) of the gas supplied to the downstream side.
[0035] The circulation flow path FS4 is provided with a cutoff
valve H4, and is connected to the exhaust/drain flow path FS6. The
exhaust/drain flow path FS6 has an exhaust/drain valve H5, which is
operated under the control of the controller EC to discharge the
impurity-containing fuel-off gas and water within the circulation
flow path FS4 to the outside. By opening the exhaust/drain valve
H5, the concentration of impurities in the fuel-off gas in the
circulation flow path FS4 is reduced, and the hydrogen
concentration in the fuel-off gas flowing through the circulation
system can consequently be increased.
[0036] The fuel-off gas discharged via the exhaust/drain valve H5
is mixed with the oxidant-off gas flowing in the oxidant-off gas
flow path AS4, and diluted by a diluter (not shown in the drawing).
Upon being driven by a motor, the circulation pump FS5 supplies the
fuel-off gas in the circulation system to the fuel cell FC in a
circulating manner.
[0037] The electric power system ES has a DC/DC converter ES1, a
battery ES2, a traction inverter ES3, a traction motor ES4 and
auxiliary devices ES5. The fuel cell system FCS is structured as a
parallel hybrid system in which the DC/DC converter ES1 and the
traction inverter ES3 are each parallel-connected to the fuel cell
FC.
[0038] The DC/DC converter ES1 has a function of increasing a
direct current voltage supplied from the battery ES2 and outputting
it to the traction inverter ES3, and also has a function of
decreasing the voltage of a direct current power generated by the
fuel cell FC or the voltage of a regenerative power collected by
the traction motor ES4 through regenerative braking and charging
the battery ES2 with the resulting power. With the above functions
of the DC/DC converter ES1, the charging and discharging of the
battery ES2 is controlled. Also, with the voltage conversion
control by the DC/DC converter ES1, the operation point (output
terminal voltage, output current) of the fuel cell FC is
controlled. A voltage sensor S1 and a current sensor S2 are
attached to the fuel cell FC. The voltage sensor S1 detects an
output terminal voltage of the fuel cell FC. The current sensor S2
detects an output current of the fuel cell FC.
[0039] The battery ES2 functions as: a source in which surplus
electric power is to be stored; a source in which regenerative
energy is to be stored during regenerative braking; and an energy
buffer to be used when the load varies as a result of acceleration
or deceleration of the fuel cell vehicle. A secondary battery, such
as a nickel/cadmium battery, a nickel/hydrogen battery, or a
lithium secondary battery, is preferably used for the battery ES2.
An SOC sensor S3 for detecting an SOC (state of charge) is attached
to the battery ES2.
[0040] The traction inverter ES3 is, for example, a PWM inverter
driven by a pulse-width modulation system. In response to control
commands from the controller EC, the traction inverter ES3 converts
a direct current voltage output from the fuel cell FC or from the
battery ES2 into a three-phase alternating current voltage, thereby
controlling the rotation torque of the traction motor ES4. The
traction motor ES4 is, for example, a three-phase AC motor, and
constitutes a power source of the fuel cell vehicle.
[0041] The term "auxiliary devices ES5" is used as a generic term
referring to various motors disposed in each portion of the fuel
cell system FCS (for example, power sources for pumps, etc.),
inverters for driving such motors, and various on-board auxiliary
units (for example, an air compressor, injector, coolant water
circulation pump, radiator, etc.).
[0042] The cooling system CS has a radiator CS1, a coolant pump
CS2, a coolant inflow path CS3 and a coolant outflow path CS4. The
radiator CS1 cools a coolant for cooling the fuel cell FC by
radiating the heat of the coolant. The coolant pump CS2 is a pump
for flowing the coolant back and forth between the fuel cell FC and
the radiator CS1. The coolant inflow path CS3 is a flow path
connecting the radiator CS1 and the fuel cell FC, and is provided
with the coolant pump CS2. When the coolant pump CS2 is driven, the
coolant flows from the radiator CS1 into the fuel cell FC through
the coolant inflow path CS3. The coolant outflow path CS4 is a flow
path connecting the fuel cell FC and the radiator CS1, and is
provided with a water temperature sensor S5. When the coolant pump
CS2 is driven, the coolant that has been used to cool down the fuel
cell FC flows back to the radiator CS1.
[0043] The controller EC (control unit) is a computer system which
is provided with a CPU, ROM, RAM and an input/output interface, and
controls the respective portions of the fuel cell system FCS. For
example, when the controller EC receives an ignition signal IG
output from an ignition switch, it starts the operation of the fuel
cell system FCS. After that, the controller EC determines the
required electric power in the entire fuel cell system FCS based
on, for example, an acceleration-opening-degree signal ACC output
from an acceleration sensor and a vehicle speed signal VC output
from a speed sensor. The required electric power in the entire fuel
cell system FCS corresponds to the sum of the electric power for
running the vehicle and the electric power for auxiliary
devices.
[0044] The above-mentioned electric power for auxiliary devices
includes: power consumed by on-board auxiliary units (a humidifier,
air compressor, hydrogen pump, coolant water circulation pump,
etc.); power consumed by devices necessary for running the vehicle
(a speed change gear, wheel controller, steering device,
suspension, etc.); and power consumed by devices arranged in a
passenger space (an air conditioner, lighting device, audio system,
etc.).
[0045] The controller EC determines what portions of the power are
to be output from the fuel cell FC and from the battery ES2,
respectively. The controller EC controls the oxidant gas supply
system ASS and the fuel gas supply system FSS so that the power
generated by the fuel cell FC corresponds to a target power, and it
also controls the DC/DC converter ES1 to control the operation
point (output terminal voltage, output current) of the fuel cell
FC. Furthermore, in order to attain a target torque depending on
the degree of opening of the accelerator, the controller EC outputs
to the traction inverter ES3, alternating current voltage command
values for the respective U, V and W phases as switching commands,
thereby controlling the output torque and the number of rotations
of the traction motor ES4. Moreover, the controller EC controls the
cooling system CS so that the fuel cell FC is at a suitable
temperature.
[0046] Next, how the fuel cell system FCS of this embodiment
determines whether a rapid warm-up operation should be continued or
not will be described with reference to FIG. 2. FIG. 2 is a
flowchart for determining whether a rapid warm-up operation should
be continued or not. In this embodiment, the "rapid warm-up
operation" means a low-efficiency operation performed with a
reduced output terminal voltage by decreasing the amount of air
supply through the drive of the air compressor AS2.
[0047] In step S01, the temperature of the fuel cell FC is
detected. This detection of the fuel cell FC temperature is carried
out by a temperature sensor (not shown in the drawing) provided in
the fuel cell FC, and the detected temperature is output to the
controller EC.
[0048] Subsequently to step S01, in step S02, an effective catalyst
area of the fuel cell FC is calculated by means of a current sweep
for the fuel cell FC for a short period of time. More specifically,
the voltage of the fuel cell FC is varied for a short period of
time (not longer than one second), thereby obtaining
current-voltage characteristics, which show the relationship
between an output terminal voltage and an output current of the
fuel cell FC. FIG. 3 shows one example of the obtained
current-voltage characteristics. In FIG. 3, WP is an operation
point where a rapid warm-up operation is carried out. In FIG. 3, S1
is a curve obtained by varying the output terminal voltage of the
fuel cell FC, and this curve S1 is almost the same as the cyclic
voltammetry (CV) curve of the unit cell constituting the fuel cell
FC.
[0049] FIG. 4 shows an example of the above-described CV curve of
the unit cell. In P1 in FIG. 4, a hydrogen reaction proceeds, and
the reaction of formula (4) below occurs in the anode while the
reaction of formula (5) below occurs in the cathode.
H.sub.2.fwdarw.2H.sup.++2e.sup.- (4)
2H.sup.++2e.sup.-.fwdarw.H.sub.2 (5)
[0050] In P2, a catalyst oxidation reaction as shown by formula (6)
below occurs, and in P3, a catalyst reduction reaction as shown by
formula (7) below occurs.
2Pt+O.sub.2.fwdarw.2PtO (6)
2PtO.fwdarw.2Pt+O.sub.2 (7)
[0051] In P4, a hydrogen reaction proceeds, and the reaction of
formula (8) below occurs in the anode while the reaction of formula
(9) below occurs in the cathode.
2H.sup.++2e.sup.-.fwdarw.H.sub.2 (8)
H.sub.2.fwdarw.2H.sup.++2e.sup.- (9)
[0052] Accordingly, in the CV curve in FIG. 4, the effective
surface area of the catalyst of platinum is obtained by calculating
an area of oxidation current which corresponds to about 0.1-0.3 V
(area of the region A2) and dividing the obtained area of oxidation
current by an electric quantity arising from hydrogen elimination
from the catalyst at about 0.1-0.3 V. In other words, the magnitude
of the area of the region A2 in FIG. 4 is indicative of the
magnitude of the effective catalyst area.
[0053] As already stated above, since the curve S1 in FIG. 3, which
is a current-voltage curve obtained through a current sweep for the
fuel cell FC for a short period of time, is almost the same as the
CV curve S2 of the unit cell constituting the fuel cell FC, the
region A1 in FIG. 3 corresponds to the region A2 in FIG. 4 and the
magnitude of the area of the region A1 is indicative of the
magnitude of the effective catalyst area. According to the above,
the effective catalyst area of the fuel cell FC is obtained.
[0054] Subsequently to step S02, in step S03, whether the fuel cell
FC temperature detected in step S01 is below 0.degree. C. and the
effective catalyst area calculated in step S02 is below a
predetermined value is judged. If the fuel cell FC is at a
temperature below 0.degree. C. and if the effective catalyst area
is below the predetermined value, the procedure goes to step S04;
and if the fuel cell FC is at a temperature equal to or higher than
0.degree. C. and if the effective catalyst area is equal to or
greater than the predetermined value, the procedure goes to step
S05.
[0055] In step S04, the rapid warm-up operation of the fuel cell FC
is continued. This is because the fuel cell FC temperature is below
0.degree. C. and the effective catalyst area is below the
predetermined value, which means that the gas flow path of the fuel
cell FC is clogged, and thus, the fuel cell FC is not prepared to
perform normal power generation.
[0056] In step S05, the rapid warm-up operation of the fuel cell FC
is stopped. This is because the fuel cell FC temperature is equal
to or higher than 0.degree. C. and the effective catalyst area is
equal to or greater than the predetermined value, which means that
no clogging occurs in the gas flow path of the fuel cell FC, and
thus, the fuel gas flows through each unit cell constituting the
fuel cell FC, and the fuel cell FC is prepared to perform normal
power generation.
[0057] The above determination method of this embodiment can also
be utilized in determining whether the circulation in the fuel gas
supply system FSS is allowed or not, or in determining whether the
circulation in the cooling system CS is allowed or not. FIG. 5 is a
flowchart showing an application of the above method to the
determination of whether the circulation in the fuel gas supply
system FSS is allowed or not, and FIG. 6 is a flowchart showing an
application of the above method to the determination of whether the
circulation in the cooling system CS is allowed or not.
[0058] Referring to FIG. 5, the procedure for determining whether
the circulation in the fuel gas supply system FSS is allowed or not
will be described. In step S11, the temperature of the fuel cell FC
is detected. This detection of the fuel cell FC temperature is
carried out by a temperature sensor (not shown in the drawing)
provided in the fuel cell FC, and the detected temperature is
output to the controller EC.
[0059] Subsequently to step S11, in step S12, an effective catalyst
area of the fuel cell FC is calculated by means of a current sweep
for the fuel cell FC for a short period of time. The method of
calculating the effective catalyst area is the same as described
above, so a detailed description will be omitted here.
[0060] Subsequently to step S12, in step S13, whether the fuel cell
FC temperature detected in step S11 is below 0.degree. C. and the
effective catalyst area calculated in step S12 is below a
predetermined value is judged. If the fuel cell FC is at a
temperature below 0.degree. C. and if the effective catalyst area
is below the predetermined value, the procedure goes to step S14;
and if the fuel cell FC is at a temperature equal to or higher than
0.degree. C. and if the effective catalyst area is equal to or
greater than the predetermined value, the procedure goes to step
S17.
[0061] In step S14, whether the effective catalyst area calculated
in step S12 is below a second predetermined value is determined.
The second predetermined value is smaller than the predetermined
value used in step S13. If the effective catalyst area is below the
second predetermined value, the procedure goes to step S15, and if
the effective catalyst area is equal to or greater than the second
predetermined value, the procedure goes to step S16.
[0062] In step S15, the circulation pump FS5 is stopped so as to
prohibit the circulation in the fuel gas supply system FSS, which
is an anode circulation system. If the effective catalyst area is
below the second predetermined value, it is suggested that clogging
in the gas flow path of the fuel cell FC further proceeds, so the
circulation pump FS5 is stopped to prohibit the flow of water,
thereby preventing still further clogging in the gas flow path.
When prohibiting the circulation in the fuel gas supply system FSS,
a decrease of hydrogen concentration would be an issue of concern;
however, since the fuel cell system is in the rapid warm-up
operation for a short period of time, the operation can be
performed without critical problems by increasing the pressure of
the fuel gas supplied from the fuel gas supply source FS1.
[0063] In step S16, the rapid warm-up operation of the fuel cell FC
is continued. This is because the fuel cell FC temperature is below
0.degree. C. and the effective catalyst area is below the
predetermined value, which means that the gas flow path of the fuel
cell FC is clogged, and thus, the fuel cell FC is not prepared to
perform normal power generation.
[0064] In step S17, the rapid warm-up operation of the fuel cell FC
is stopped. This is because the fuel cell FC temperature is equal
to or higher than 0.degree. C. and the effective catalyst area is
equal to or greater than the predetermined value, which means that
no clogging occurs in the gas flow path of the fuel cell FC, and
thus, the fuel gas flows through each unit cell constituting the
fuel cell FC, and the fuel cell FC is prepared to perform normal
power generation.
[0065] Referring next to FIG. 6, the procedure for determining
whether the circulation in the cooling system CS is allowed or not
will be described. In step S21, the temperature of the fuel cell FC
is detected. This detection of the fuel cell FC temperature is
carried out by a temperature sensor (not shown in the drawing)
provided in the fuel cell FC, and the detected temperature is
output to the controller EC.
[0066] Subsequently to step S21, in step S22, an effective catalyst
area of the fuel cell FC is calculated by means of a current sweep
for the fuel cell FC for a short period of time. The method of
calculating the effective catalyst area is the same as described
above, so a detailed description will be omitted here.
[0067] Subsequently to step S22, in step S23, whether the fuel cell
FC temperature detected in step S21 is below 0.degree. C. and the
effective catalyst area calculated in step S22 is below a
predetermined value is judged. If the fuel cell FC is at a
temperature below 0.degree. C. and if the effective catalyst area
is below the predetermined value, the procedure goes to step S24;
and if the fuel cell FC is at a temperature equal to or higher than
0.degree. C. and if the effective catalyst area is equal to or
greater than the predetermined value, the procedure goes to step
S27.
[0068] In step S24, whether the effective catalyst area calculated
in step S22 is below a second predetermined value is determined.
The second predetermined value is smaller than the predetermined
value used in step S23. If the effective catalyst area is below the
second predetermined value, the procedure goes to step S25, and if
the effective catalyst area is equal to or greater than the second
predetermined value, the procedure goes to step S26.
[0069] In step S25, the coolant pump CS2 is stopped so as to
prohibit the circulation in the cooling system CS. If the effective
catalyst area is below the second predetermined value, it is
suggested that clogging in the gas flow path of the fuel cell FC
further proceeds, so the coolant pump CS2 is stopped so as to
reduce a heat capacity, thereby giving priority to the warm-up.
When prohibiting the circulation in the cooling system CS, a local
increase of temperature would be an issue of concern; however,
since it is considered that the reaction in the catalyst does not
proceed so much in the case where the effective catalyst area is
below the second predetermined value, it is preferable that
priority is given to the warm-up.
[0070] In step S26, the rapid warm-up operation of the fuel cell FC
is continued. This is because the fuel cell FC temperature is below
0.degree. C. and the effective catalyst area is below the
predetermined value, which means that the gas flow path of the fuel
cell FC is clogged, and thus, the fuel cell FC is not prepared to
perform normal power generation.
[0071] In step S27, the rapid warm-up operation of the fuel cell FC
is stopped. This is because the fuel cell FC temperature is equal
to or higher than 0.degree. C. and the effective catalyst area is
equal to or greater than the predetermined value, which means that
no clogging occurs in the gas flow path of the fuel cell FC, and
thus, the fuel gas flows through each unit cell constituting the
fuel cell FC, and the fuel cell FC is prepared to perform normal
power generation.
DESCRIPTION OF REFERENCE NUMERALS
[0072] FCS: fuel cell system
[0073] FC: fuel cell
[0074] ASS: oxidant gas supply system
[0075] AS1: filter
[0076] AS2: air compressor
[0077] AS3: oxidant gas flow path
[0078] AS4: oxidant-off gas flow path
[0079] AS5: humidifier
[0080] A3: back pressure regulating valve
[0081] CS: cooling system
[0082] CS1: radiator
[0083] CS2: coolant pump
[0084] CS3: coolant inflow path
[0085] CS4: coolant outflow path
[0086] FSS: fuel gas supply system
[0087] FS1: fuel gas supply source
[0088] FS2: injector
[0089] FS3: fuel gas flow path
[0090] FS4: circulation flow path
[0091] FS5: circulation pump
[0092] FS6: exhaust/drain flow path
[0093] H1: cutoff valve
[0094] H2: regulator
[0095] H3: cutoff valve
[0096] H4: cutoff valve
[0097] H5: exhaust/drain valve
[0098] ES: electric power system
[0099] ES1: DC/DC converter
[0100] ES2: battery
[0101] ES3: traction inverter
[0102] ES4: traction motor
[0103] ES5: auxiliary devices
[0104] EC: controller
[0105] S1: voltage sensor
[0106] S2: current sensor
[0107] S3: SOC sensor
[0108] S4: pressure sensor
[0109] S5: water temperature sensor
[0110] ACC: acceleration-opening-degree signal
[0111] IG: ignition signal
[0112] VC: vehicle speed signal
* * * * *